Refractometer



Auge 21, 1945. M, 'SILGE 2,383,347

REFRACTOMETER Filed Sept. 21, 1942 MART/N SILGE.

/ E z"g INVENToR, I

rm/wer l with editable targettheytelescope'fof` PatenteclAug. 2L 194115" y me NT4, omc-E, y

nEFnAoToMe'rErt t p,resent inventiizinA relates improvements in effractometers, and'` has: particular i reference refractometers. `luSed measuringl the light sernifselifdjs"and"l solids tojestablish certain physica properties ofsufclfi samples; Refractometers ofmthisytype arefbased" on the. principle yofjtotal ith yindex prism and tele'- `sfeope arranged `so;thatcne unit maybe moved y Martin silge, oaluahaoalif. "istantanea september 21,1942, serial No. 459,139

i solaires.`

i borderline, `off total freflection is `observed' 'through the" telescope Y and; isfbrought into' coincidence nithe telescope. The an.- gular displacement ObServed' between the. ndeir group comprises suclrrefractometers asf the Abbe,

servestoreaddirectly the position `ofthe borderlinearrotaiprefieuon eftnesampije. Thi-sgrouphowever; is necessarilyflirnitedl because of the in? herentdeflcijncies* i ical i l i dies, *racks and pininsV e Sushi rectifefict fon the* accuracy and dependability of these instruments. ,i l l y v leiractometersfof11 the (b)- groupdcrnot4 require moving -mechanicalf parts "fori-'the purpose of dewtermimet i `reiieetioxr becaiusertheiimage "of thelattenis* cast" e; position `@tiene borderline of total wherefi i read {through `ltliej ocular.l non@ i this imageisentirdy a] function` of the refractive@indexl of the sampler being" `ineasured andI the #opticabl' properties? of the in'dexfprisin and refractive indices@M or corresponding; valuessuchA rnechanprisni and' the'itelescope",theirr isn.translated'int()` accuracy is largely `controlled `by ,the` telescope rnagniication.` The higher the lati'ie'r,` the greater the relative displacementofy the .image of the. borderline of total reiiectionior two neighboring refractiveindices, which .in` .turn permits higher i reading accuracy against scale divisions. Dipping (immersion) refractometers, ,utilizing this" principleare built to read` therefractive index. nDfreliably to Within a few units `of the, fth decimal and are considered the most accurate of commercial refractometers. This accuracy could, no doubt, be increased `further :by the use of still higher telescope magnifcatiohs.

However, since, everything else being equal, the

eld'of View of atelesoope is approximately in-` versely proportional.` to its..rnagniiicatien,U the measuring range of refractometers. invthis` group` is limited; and in no case can,- it be Vgreater than the range ofv refractive Iindicesernbraced by the' scale `inthe ocular. i t

Inl order to increase; the totalrange of such refractometers, a whole serieslof..interclnauge-` able indexuprisms, made of glass'iof differentrefractive-indices and of differing refractive angles,` f

have been` provided. Each change;v of prism;`

however, requires a rre-calibration of the instru:

ment; is awkward and may `cause.damages` This l method, therefore, has `not becomepomilar,` and i its use is, confined to research 1aboratories.I,1ti tlei-use `is Amade' of it in'` productioncontroll,. as seems toipreclude the use of 3 unskilledtechnicians, i 1

InJ certain so-called hand-refractometers l based on thev principle of the (brgroup, a comparatively low telescope magnification` is eme` ployedand no provision-is made=fori the inter--` changeability. of the index prism..` But,` in spite; ofthe lower telescope magncation, the measure ing range of these handz-refractometers gisr l not suiiicient to cover allfrequirements of the-various users, and it has been found `necessary,there fore,`to develop/a numberroffsuch instruments, each covering a` diierent range;V 'i

l In the presentinventionl itisproposed toy provide a refractometerwhich combinesnthe advangroups, while avoiding theV 'disadvantages of either. l I

'More particularly it is proposed` to combine an commanding` consecutive, possibly I `overlapping ranges of refractive power withl a telescope containing' Ia seriesof:` xed scalesjoff. consecutive ranges cooperable with thedifferentirangescovw f Cried by index prism. It c is the: purpose 110i index prismy having refracting characteristics `my invention, I wish to these scales to indicate the refractive index or other desired properties, such as percentage of sugar content, of the objects under observation on the particular scale corresponding to the portion each objectivel cooperating with the respective prism section and the corresponding scale to form an image of the borderline of total reflection on the latter.

My refractometer thus covers a wide range of refractive indices, but still forms a single xed unit requiring no movable parts for the purpose of finding the relative positions of the borderline of total reflection.

Further objects and advantages of my invention will appear as the specication proceeds and the' novel features of the invention will be fully set forth in the claims hereto attached. l s

The preferred form ofV my inventionis il1us trated in the accompanying drawing, forming part of this applicatiomin which: s y

Figure 1 shows schematically a longitudinal section through my refractometer;

Figure 2, an enlarged schematic view, in plan, of the optical partsv of my device;

Figure 3, a similar View showing the optical parts in elevation;

Figure 4, a. rear elevation. of the prism shown in Figures 1, 2 and 3;

Figures 5, 6 and 7, front elevations, respectively of va multi-objective, a multi-scale lens and a multi-eye lens used in my device;

` Figure 8, aperspective view of a modied form of prism adapted for use in my refractometer;

Figure 9 a perspective view of a still further modied form of prism; and

Figure 10, a schematic arrangement of'parts in which the telescope is mounted at an angle with respect to the prism. i

While I have shown only the preferred forms of 4 have it understood that various changes or modifications may be made within the scope of the claims hereto attached, without departing from the spirit'of the invention.

Referring to the drawing in detail, my refractometer I'coniprises'a telescope2 having a prism 3 at its outerend, fan ocular with a multi-eye lens 4 and airnulti-scale'lens 6 at its inner end, and a multi-objective 5 interposed between the prism and the ocular at proper distances.

The prism '3' is shown in different views in lFigures l to '74, respectively, and comprises aunitary prism structure consisting of three adjacent sections. The sections have a common entrance face I9 on whichithe sample under observation is disposed, as at I'I. The rearor exit faces I2, I3 and I4 of the three sections refracting angles with the entrance faces.

When a ray forming the borderline of total reiiection, enters the prism at the entrance face, it is refracted, and as it leaves through the rear face,

, it is againrefracted, the total refraction depending upon the refractive indexy of the sample under observation, the refractive index of the prism and the refracting angle. Since the angles a, b, and c vary in the three sections of the prism, it is apparent that each section kwill emit its range of rays at an angle different from that of the other sections. The angles are arranged so that the different prism vsections command consecutive and partly overlapping ranges.

The refracted rayspass to the objective 5 which differ and form differentA serves the purpose of forming an image of the borderline of total reflection on the scale 6, where its position in scale divisions may be read. The objective is divided into a number of parallel sections I5, I6 and II, corresponding to the sections of the prism, each section of the objective cooperating with a section of the prism. It is desirable, of course, to have the sections of the objective mounted in a single unit and in the same plane.

The scale lens 6 is similarly divided into three sections, I8, I9 and 20, and these sections are made to cooperate individually with the three sections of the objective and the three sections of the prism in such a manner that each scale section receives an image `of the borderline of total reiiection from its respective prism section only through a limited portion of the total range of said prism. Assuming, for instance, that for the device as a whole, a total range of nD 1.3 to 1.55 is desired, which is slightly more than the total range required for establishing the sugar content of a liquid, the refractive index of pure water being approximately nD 1.33, and that of, pure sugar being approximately 11D 1.55: If the central prism section I3 alone were used, as in the conventional refractometer, the total range of rays formingv the borderline of total reflection emanating from the rear face might spread fan-wise, in a given example, over an angle of 30 degrees, the exact position of the borderline within that angle depending on the refractive index of the. sample under observation. This total range would be impractical to utilize in connection with a single scale, due to inherent limitations in the dimensions of the telescope and its eld of view at magnifications required forv accurate readings. It'is proposed, therefore, in the present invention, to' split the total range into a numberof parts, three being selected for the purposes of example only,

and to conne the central scale section to cooper-l ative reading' with a limited portion of the entire range of the central prism section, preferably, of-

grees of the central prism I3 into three parts,

each comprising ten degrees` only. The central scale section I9,.in. Figure 6, would be arranged and calibrated to receive the image of the border-- line of. total reflection only if the refractive index of the sample under observation falls withiny the central range. We have, assumed -that thel total range of the refractometer is to cover re.

fractive indices of the samples between 71D 1.3 and 1.55, which might be conveniently subdivided into three sub-ranges equivalent to those refrac-Y tive indices that happen to fall within the three consecutive angles of ten degrees each. In the example underdiscussion, the central scale section would show the typical borderline of total reflection only if the sample falls within the middle range of 10 to 20 degrees, while for the two outeri ranges'the. central scale would show either light or dark, dependingupon whether the index of the sample is higher orlower than the cen,-

tral range.

The two outer sections I8 and 2U of the scale eration, it is desirable that ythey be placed alongside of the central section within a rather `limited-r eld, as illustrated in Figure 6. To allow of such.

positioning, it isnecessary that the `tWoouter ascesa? prism .i sections'. l 2:.'and1 :I4 ybe arrangedzso` that` the centerline `of.theirangelet-rays `issuing-from n each strikes@ itsicooperativ scale section:- atrthe. center .-.Wef..:a:ssumed.itha .,thektotalrangd ofirayswenranatinggifromthe'. centrali; sectiom of the i prism:` eir-` tendedi; overnam angle 1off.30sdegree`s corresponding to i al; total range` of. refractivezlindices .from'nD: 1.3

to@ 1.551 i Theincentral'scaiefsection1-takes= care .of. v .thea:centralzitexrfdegreesi covering'th'e :equivalent the? desired result; 'It is also: possible, `of. course; tocombine'.` variations in `refracting` langlesfwitn:` variation: `refractive 'indices in: the .1 .threey sections'iforthesame purpose. i .'Ilhe 'same' principle may beiA employed whereuit.

` isdesired,` for convenience ofobservation, to'arw range` the` telescopes. at; an angle `toi the prismi las` imFigure 10'; where'a suitable reiiector4 21 isvusedi coverftiie.refractiverindices:,eorrespondingntd the i angles `embracedllihsy.` thosersections to be taken. carefcofa by;V the?` `twofouteraprisin sections and the comespo'nding.Y two'` outer sealef sections. While' tl'xefcen-tral eprism.-section:issxdesigned:ltoliproject the. centerlinei cris its :tota-l ranger uponL the center i of the central scale section, the `twcifout'er.prism; sections.taei'dsigned to project the respective centerlines of the two outer ten degree positions of the total range `of `emerging rays upon the ref spective `centers of the two outer scale sections, each of `the outer scale sections being limited to a range of `lildcgrees, that is 5 degrees on opposite sides of each centerline.

In this manner` the first section I2 of the prism cooperates with the rst scale section I8 in indicating the image of the borderline of total reflection, where the refractive index of the sample falls within the first 10 degrees of the total range of degrees, while theisecond prism section cooperates with the second scale section where the refractive index falls within the second 10 der fgrees ofthe total range of 30 degrees; and the thirdffprism section cooperates with the third scale section to take care of the third 10 degrees ofthe total range of .30 degrees and their corresponding refractive indices.

, Thus, when t'h`e refractive indexof the sample 1 ."happens to be such asto cause .the borderline of total reflection to appear in the center of the second scale section, the first scale section and the bottom of the second section will appear dark, while theupper portion of the second section and the third secti-on remain light.,

The exact `shape of the three prism sec-tions l' and their refractive angles can be found by calculation. I find, for instance, under a given set` `of circumstanceslthat if the refractive angle b of the central prismsection is assumed to be 61,

the corresponding refractive `'angles a and c of the two outer sectionsshould be approximately '72` andirespectively, when using glass of a refractive index of nD.=1.65. The exact angle, of course, depends also upon the distance between the prism and the scale lens,` that is, the optical properties of the telescope.

` Similar results `may be i btained by arranging the prism as illustrated in Figure 8, in which .the

three sectionsZ l, 22 and 23 are positioned in vertical order instead of sidegby side relation.. In this case the three ranges of emerging rays would spread fan-wise and the corresponding scale sec,- tions might' be arranged in similar order to catch portions of the rays emerging from each prism section, or suitable refraoting 0r reflecting means might be provided for converging the different ranges of rays to -allowof side by side arrangement of the scalesections ina concentrated area.

`Another possible modification of prism is illustrated in Figure 9, in which the three` prism sec- 3 tions `24, `2li` and` 26 have the same` refracting angle,.butare made off material of diiferent refractive indices in the three sections to produce i ter case.

toadivertxthelfrays'inthe proper direction: i 4

The index prism maybe` made; ofi one piece of glass,` or becomposed of afpluralisty of pieces, either cemented-f together oriseparated from eachi other., andf` glass* of they samey or different refraca tive 'indices foreach-of the units may befused.

` Inftheflattercasethe refractive angles could be` alike or` could differ from each o-there-all of which'I would depend on the specific tasks* the refracA` tonieterhas to'perform-.f Y

ltilis the'purposeofthe new design to` divide the l total." measuring' rangeof the'index prism inas manyconsecutive portions as will be necessary in grder to cover each of them by a separate ocular scale. `Since the length' of such a scale `is limited to `the eld of vision of the telescope in conjunction with which it is to be used, and since this field of` view is: largely determined by the magnification Ioi the telescope, it follows that the i latter, to a large extent, will also determine the number of scales required in orderto distribute over them the total measuring range of the refractometer.

The number of scales obviouslywill determine the construction Iof the index prism, the number and arrangement of rear surface sections, the

appert'aining refractive angles and the type of r glass or glasses from which it is to be made.

While, for example,` the demands upon the reading accuracy made on a hand-refractometer,

are moderate, and a low telescope magnification l with' a large `field of view would be sufficient,

the demands in the case of a research refractometer would be much more exacting, meaning that a high telescope magnification would have to be used inY order to attain the desired accuracy. While in the former case, two 0r three scales would sunce, more would be required in th'e lat- I claim:

1. A refractometer comprising a rigid housing, a series of `spaced scales of consecutive values mounted in a limited eld in said housing, a refracting means rigidly mounted in the housing in operativerelation` to `the scales for refracting .Y rays passing through samples under observation` in` accordance `with the refractive indices of the samples, the refracting means comprising a plurality of xed sections of different refractive powers for splitting the total range of refracted' rays passing therethrough into a series of subranges of consecutive sample index values corresponding `to the scale values and for directing the sub-ranges toward the corresponding scales, and rigid means interposed `between the refracting means and .the scales for rendering the sub-` `ranges of refracted rays readable on the scales of corresponding measuring values, whereby the refractometer ismade to selectively register the index value of any sample within the total `range rays passing through samples under observation in accordance with the refractive indices ofthe samples, the refracting means comprising a plurality of xed sections of different refractive angles for splitting the total range of refracted rays passing therethrough into a series of subranges of consecutive sample index values corresponding to the scale values, and for directing the sub-ranges toward the corresponding scales, and rigid means interposed between the refracting means and the scales for rendering the subranges of refracted rays readable on the scales of corresponding measuring values, whereby the refractometer is made to selectively register the index value of any sample within the total-range Qn'one of the scales without requiringmechanical adjustment.

3. A refractometer comprising a rigid housing, a series of spaced scales of consecutive values mounted in a limited field in said housing, a 20 refracting means rigidly mounted in the housing in operative relation to the scales for refracting rays passing through samples under observation in accordance with the refractive indices ofthe samples, the refracting means comprising a plurality of xed sections of ldifferent'refractive indices forv splitting the total range Iof refracted rays passing therethrough into a series of4 subrangesof consecutive sample. index values corresponding to the scale values, and for directing the suberanges toward' the corresponding scales, and rigid means interposed between the refracting means and the scales for rendering the subranges of retracted rays readable on the scales ofy corresponding measuring Values, whereby the refractometer is made tok selectively register the indexvalue of any sample within the total range on one of the scales without requiring mechanical adjustment.

MAR'I'IN SILGE. 

